Various means for improving rolling resistance of a tire to improve energy conservation, and for improving steering stability of a vehicle have been proposed. One of such means is to make a tread of a tire with a two-layered structure (inner layer and outer layer) and use a rubber composition, which is excellent in rolling resistance and steering stability, for a base tread that is the inner layer.
JP 4402566 B and JP 4510778 B describe that a rubber composition for a base tread which is excellent in steering stability and rolling resistance can be obtained by using a rubber component comprising: (a) 20 to 60% by weight of a polybutadiene rubber comprising 2.5 to 20% by weight of 1,2-syndiotactic polybutadiene crystal; (b) 5 to 80% by weight of a tin-modified polybutadiene rubber prepared by polymerization with a lithium initiator and having a content of tin atoms of 50 to 3,000 ppm, a vinyl bond amount of 5 to 50% by weight and a molecular weight distribution (Mw/Mn) of not more than 2.0; and (c) 10 to 75% by weight of a rubber other than (a) and (b). However, for achieving a good balance among steering stability, rolling resistance and durability, there is room for improvement.